The invention is based on an rpm governor for fuel injection pumps of internal combustion engines as generally defined hereinafter. As the combustion quality required of Diesel engines increases, in terms of fuel consumption on the one hand and the quality of the exhaust gases on the other, electric speed governors are increasingly used, because engine and environmental parameters can be converted into set-point values much more accurately and quickly with an electronic control unit than with mechanical governors. There are still problems, however, in generating the relatively large adjusting forces and performing breakaway regulation when the allowable maximum rpm has been reached, so as to prevent racing of the engine; also, especially during starting and when the engine is cold, a controlled increased injection quantity is necessary in order to attain engine concentricity.
In a known speed governor of the above general type (British Pat. No. 2,073,448), the variable position of the quantity control member is measured via a transducer disposed in the control motor; the transducer operates like a potentiometer and supplies an electrical signal representing the actual position of the control motor adjusting member to the electric control unit. A two-part lever that is pivotable about an adjustable shaft is disposed between the control motor and the quantity control member, so that when the drag member part that is connected to the quantity control member meets the travel limiting means, the quantity control member can no longer be displaced further, yet the control motor need not stop as a result. Thus the position feedback means provides actual information to the electric control unit only about the position of the adjusting member of the control motor, not about the position of the quantity control member. Although the maximum rpm is limited by the travel limiting means in this known speed governor, it is not clear how the increased starting fuel quantity can be controlled with a governor of this kind.
In another known speed governor of the above general type, the entire rpm range, including starting and full load, is controlled via the electric control motor, which involves the danger of engine racing. For safety's sake, a bypass can be opened up via a magnetic valve, interrupting the fuel injection; however, this functions only if an electrical interruption occurs, for instance if the electricity fails. Certainly this feature is often undesirable in Diesel engines as a means of enabling emergency operation, even if it were only to be provided in the maximum rpm range, that is, by means of the full-load stop.
In any event, for speed governors having electric control motors it is very expensive to detect the actual statuses for starting and full-load quantity via an electrical position transducer, and from these values to regulate an allowable actual quantity using the electronic control unit.